The present invention relates to aqueous suspensions and slurries of iron oxide pigments.
In the manufacture of colored concrete products such as interlocking concrete pavers, concrete blocks, concrete roofing tiles, etc., the color is often imparted by using pigment suspensions or slurries. Use of such suspensions and slurries makes it easier under certain circumstances (e.g., inadequate concrete mixer) to mix the pigment with the concrete to obtain a homogeneous color. The use of a liquid rather than a powdery pigment composition results in less dust and less of a nuisance to construction workers.
Because iron oxide pigments are available in shades ranging from yellow to orange to red to brown to black, iron oxide slurries and suspensions are commonly used in coloring applications. However, the pigments in the available slurries and suspensions tend to settle out upon standing. It is therefore necessary to remix the slurry or suspension before use to ensure homogeneity of color. Such remixing is not however always readily accomplished due to the pseudoplastic nature of the slurry.
Concentrated slurries and dispersions of iron oxides are economically advantageous because they occupy a smaller volume and require less storage space than more dilute slurries and dispersions. However, there is a limit to solids concentration beyond which the dispersion ceases to be fluid. It would therefore be economically advantageous to raise this limit of solids concentration as high as possible.